1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
|
//===- SimplifyCFG.cpp - CFG Simplification Routines -------------*- C++ -*--=//
//
// This file provides several routines that are useful for simplifying CFGs in
// various ways...
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/SimplifyCFG.h"
#include "llvm/BasicBlock.h"
#include "llvm/Method.h"
#include "llvm/iTerminators.h"
#include "llvm/iOther.h"
#include "llvm/Type.h"
// UnifyAllExitNodes - Unify all exit nodes of the CFG by creating a new
// BasicBlock, and converting all returns to unconditional branches to this
// new basic block. The singular exit node is returned.
//
// If there are no return stmts in the Method, a null pointer is returned.
//
BasicBlock *cfg::UnifyAllExitNodes(Method *M) {
vector<BasicBlock*> ReturningBlocks;
// Loop over all of the blocks in a method, tracking all of the blocks that
// return.
//
for(Method::iterator I = M->begin(), E = M->end(); I != E; ++I)
if ((*I)->getTerminator()->getInstType() == Instruction::Ret)
ReturningBlocks.push_back(*I);
if (ReturningBlocks.size() == 0)
return 0; // No blocks return
else if (ReturningBlocks.size() == 1)
return ReturningBlocks.front(); // Already has a single return block
// Otherwise, we need to insert a new basic block into the method, add a PHI
// node (if the function returns a value), and convert all of the return
// instructions into unconditional branches.
//
BasicBlock *NewRetBlock = new BasicBlock("", M);
if (M->getReturnType() != Type::VoidTy) {
// If the method doesn't return void... add a PHI node to the block...
PHINode *PN = new PHINode(M->getReturnType());
NewRetBlock->getInstList().push_back(PN);
// Add an incoming element to the PHI node for every return instruction that
// is merging into this new block...
for (vector<BasicBlock*>::iterator I = ReturningBlocks.begin(),
E = ReturningBlocks.end(); I != E; ++I)
PN->addIncoming((*I)->getTerminator()->getOperand(0), *I);
// Add a return instruction to return the result of the PHI node...
NewRetBlock->getInstList().push_back(new ReturnInst(PN));
} else {
// If it returns void, just add a return void instruction to the block
NewRetBlock->getInstList().push_back(new ReturnInst());
}
// Loop over all of the blocks, replacing the return instruction with an
// unconditional branch.
//
for (vector<BasicBlock*>::iterator I = ReturningBlocks.begin(),
E = ReturningBlocks.end(); I != E; ++I) {
delete (*I)->getInstList().pop_back(); // Remove the return insn
(*I)->getInstList().push_back(new BranchInst(NewRetBlock));
}
return NewRetBlock;
}
|
